The invention concerns a vacuum membrane pump, respectively a head portion for a vacuum membrane pump, according to the preamble to the independent patent claims.
Membrane pumps with an elastic membrane engaging with a counterpart to form a seal, and with a pump chamber being defined between counterpart and membrane, are state of the art. In general, an inlet and an outlet valve open into the pump chamber. The membrane is moved by means of a cam in such a way that the volume of said chamber is periodically reduced and enlarged. On enlargement of the volume, air is drawn in via the inlet valve, said air being expelled via the outlet or exhaust valve on reduction of said volume. In this way, pressurization and a partial vacuum can be imparted to gaseous media.
Mainly when using membrane pumps for the creation of a vacuum, great demands are placed on the materials of the components used. In particular, solvents contained in a gas shall not be permitted to accumulate on the surface of the membrane and/or the counterpart. The membrane must be both flexible and gastight while, at minimum volume, the counterpart should have a complementary form that exactly corresponds to the form of the membrane. In order to create the greatest possible efficiency, the volume of the pump chamber should assume the smallest possible value on completion of the expulsion sequence.
Membrane pumps are, for example, disclosed in DE 40 07 932 A1, DE 28 51 060 A1 and EP 072 275 A1. DE 40 07 932 discloses a membrane pump with a reinforced shaped membrane at its centre; DE 28 51 060 shows a membrane pump possessing two pump chambers separated by a single membrane; and EP 072 275 shows a vacuum pump with a special distribution arrangement for the inlet and outlet valves.
All such state-of-the-art membrane pumps possess various drawbacks, however. In particular, the membrane and the counterpart must be subjected to surface treatment which results in complex and expensive manufacture. Plastic materials used for the counterpart are not necessarily form-stable, and without surface treatment will frequently absorb solvents which can be released again when a vacuum is created.
A further drawback of state-of-the-art pumps is their complicated construction. The individual parts must be connected together to form a seal, and until now this has required the use of many separate components such as seals, screws and clamps.